The birth notice has been driven to Buckingham Palace, while The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall, Prince Harry, as well as members of the Middleton family have been informed.

The new royal baby is the Queen’s third great-grandchild and is destined to be crowned monarch.

Members of the public gathered outside The Lindo Wing of London’s St Mary’s Hospital after the Duchess of Cambridge went into labour on July 22.

Photo: Getty Images

Kate was tended to by a top medical team led by the Queen’s former gynaecologist Marcus Setchell, who delivered the Countess of Wessex’s two children.

A Buckingham Palace spokesman said: “The Queen and Duke of Edinburgh are delighted at the news.”

The Prince of Wales also released a statement revealing his delight.

“Both my wife and I are overjoyed at the arrival of my first grandchild,” Charles said in a statement released by Clarence House.

A formal notice of the birth has been be posted on the forecourt of Buckingham Palace to the cheers of thousands of spectators outside the gates.

In this image from television, the official announcement of the birth of the son of the Duke and Duchess of Cambridge is posted at the gates of Buckingham Palace.

Photo: AP

Crowds gathered outside the hospital where the Duchess of Cambridge gave birth also cheered the arrival of the baby boy, as might betting agencies.

Many punters believed William and Kate would have girl and put their money on the name. The favourite was Alexandra, although other monikers that have attracted royal fans include Charlotte, Diana, Elizabeth and Victoria.

George and James were most popular among those who thought the new baby would be a boy.

The Duke was known to want a daughter, while the Duchess had hoped for a son. Her Royal Highness and her son will remain in hospital overnight